Core drilling is used to collect a core sample from a subsurface formation that can be analyzed to determine the composition of the formation. To collect the core sample, a core drill string is lowered into a borehole traversing the formation. The core drill string typically includes a drill stem with an annular drill bit appended at an end thereof for cutting the formation. A core tube assembly is disposed within the drill stem to collect the core sample from the formation. In wireline core drilling, the core tube assembly can be retrieved from the drill stem without removing the core drill string from the borehole. This allows multiple core samples to be collected without removing the core drill string from the borehole in between each collection of core sample. The core tube assembly is run into the drill stem at the end of an overshot attached to a wireline. The core tube assembly can be retrieved from the drill stem by pulling back the wireline.
U.S. Pat. No. 3,701,389 (Egnelov et al., Oct. 31, 1972) discloses a retrievable inner core tube assembly with means for releasably locking the inner core tube assembly to a drill stem. In this patent, the inner core tube assembly includes an inner core tube, an intermediate piece, and a housing. Two latch dogs, pivotally mounted on a stub axle, are disposed in the housing. Each latch dog has two arms. One of the arms on each latch dog is arranged to engage a retrieving device while the other of the arms on each latch dog is arranged to lock the inner core tube assembly to the drill stem when the inner core tube assembly is inserted in the drill stem.